1. Field of the Invention
An aspect of the present invention relates to a centrifuge, and more particularly to a pulsed operation function thereof in which the centrifuge is operated for a short time period to drop liquid droplets adhering to a sidewall in a sample container, in a high-speed centrifuge using a vacuum pump.
2. Description of the Related Art
Centrifuges are used in many fields such as the medical, pharmaceutical, and genetic engineering fields. For example, a wide variety of centrifuges ranging from those operating at 10,000 to 30,000 rpm under atmospheric pressure to those operating at 30,000 to 150,000 rpm are commercialized. In a high-speed centrifuge rotating at 30,000 rpm or more, the rotor is rotated while reducing the rotor chamber pressure by a vacuum pump to avoid heat generation of the rotor due to air friction. Usually, an oil-sealed rotary vacuum pump is used as a vacuum pump, and an oil diffusion vacuum pump is connected in series to assist the oil-sealed rotary vacuum pump. Depending on a sample to be centrifuged, separation may be performed while maintaining the sample at a temperature (for example, 4° C.) lower than room temperature. Therefore, a cooling device is disposed in the rotor chamber. Further, an air leak valve is disposed to introduce air into the rotor chamber for taking the rotor out from the evacuated rotor chamber.
When air is accidentally introduced into the rotor chamber in which the rotor is rotated at high speed, the rotor may generate heat to deteriorate the sample in the rotor. Further, depending on the rotation speed of the rotor, the rotor may be subjected to a lift force due to air turbulence, and the rotation of the rotor may be not stabilized. In order to prevent air from entering the rotor chamber even when, for example, an electrical power failure accidentally occurs, the air leak valve is often configured to be opened by an operation of a solenoid only when the solenoid is energized. In order to prevent the air leak valve from being opened during rotation by an erroneous operation of a control device, as a safety measure, control signals may be duplicated. A door lock mechanism which locks a door so as not to be opened during rotation is disposed to prevent the door from being accidentally opened to allow the hand to touch the rotor which is being rotated at high speed.
In a normal use of the above-described centrifuge, when the user sets the rotor, closes the door, and presses a start button, the door is locked by the door lock mechanism, the vacuum pump operates to start depressurization of the chamber, and then the rotor begins to rotate. In a centrifuge capable of rotating at a high speed of 30,000 rpm or more, in order to prevent the temperature increase by windage loss, the rotor is operated at low speed with limiting the rotation speed to about 5,000 rpm until the vacuum degree reaches a predetermined level, and, after the vacuum degree reaches the predetermined level, the rotor rotation is accelerated to the preset rotation speed. When the rotor reaches the user-preset rotation speed, the constant speed operation is performed. When the user-preset time period elapses or the user presses a stop button, the rotor is decelerated and stopped. The user performs a predetermined operation to cause the air leak valve to be opened, thereby releasing the door lock, and then takes out the rotor.
For example, a reagent or its liquid droplets adhering to the inner sidewall of a sample container tube is dropped onto the bottom thereof by being shaken by a hand in order to enhance the accuracy of the mixture ratio. Sometimes, the centrifuge is used instead of shaking the sample container tube. Such method is disclosed in, for example, JP-2002-113391-A. In the case, the rotor is operated only for a short time period to drop liquid droplets. In a centrifuge not having a vacuum pump and being capable of rotating only at 20,000 rpm or less, such a uses is well known as “pulsed operation” or “instantaneous centrifugal function”. In the pulsed operation, a centrifuge is often used at a relatively low speed of about 15,000 rpm or less. Recently, a centrifuge having a switch for a pulsed operation mode has been put into practical use.
Unlike the normal centrifugal operation, in the pulsed operation, the rotor is required to reach a predetermined rotation speed, it is not important to maintain the rotation speed for a long time period, and it is usual to immediately reduce the speed. Therefore, a centrifuge has been commercially available which has a function of, only during a period when a pulsed operation button is pressed, operating the rotor in an accelerated or constant speed state, and, when the pulsed operation button is released, immediately starting deceleration to stop the rotor, or that of, when the pulsed operation button is pressed, accelerating to a predetermined rotation speed, and, immediately after the acceleration, decelerating or stopping the rotation.
However, the inventors have noted that a trouble occurs when a vacuum-pump-equipped centrifuge is similarly provided with the pulsed operation function. In the vacuum-pump-equipped centrifuge, the vacuum pump is automatically operated with the start of the rotation of the rotor, and hence a step which continues for several seconds, and in which, after the stop of the pulsed operation, an air leak valve is opened and the pressure in a chamber is returned to the atmospheric pressure is required. The pulsed operation requires merely ten to several tens of seconds. Therefore, when the above-mentioned step of returning the pressure in the chamber to the atmospheric pressure is added, the working efficiency is largely decreased. Since the pulsed operation itself requires a low rotation speed, it is not necessary to set the vacuum state. When operating the vacuum pump, in order to prevent evaporation of the sample from being caused by the vacuum state of the chamber, or freezing by releasing of heat of vaporization from occurring, a cover should be surely closed. Each time when an insignificant work of the pulsed operation is to be performed, therefore, the cover must be attached, thereby deteriorating the workability.